1. Field of the Invention
This invention relates to a developing device which is used in an electrophotography system or the like, and more particularly to a developing device for developing an electrostatic latent image formed on a latent image carrier, using toner. More particularly, the invention relates to a developing device for performing the developing process while forming a uniform and thin toner layer on a toner carrier.
2. Prior Art
As disclosed in Unexamined Japanese patent publications Nos. SHO 47-13,088 and SHO 47-13,089, in a conventional developing device, a toner carrier which is lined by a foamed member and in which a soft electrically conductive layer is formed on the foamed member carries toner to develop a latent image.
Japanese Unexamined patent publication No. SHO 55-77,764 discloses another developing device in which a toner carrier using a foam material carries toner to develop a latent image.
Japanese unexamnined patent publication No. SHO 52-125,340 discloses a further developing device which comprises a toner carrier having a rubber surface for carrying toner and developing a latent image, and an adjust member for eliminating level irregularities of a toner layer on the toner carrier after the developing process.
Japanese Unexamined patent publication No. HEI 3-155,575 discloses a still further developing device in which the surface layer of a supply member is formed by polyurethane foam and the cell diameter of the polyurethane foam is set to be 30 to 200 .mu.m.
Japanese Unexamined patent publication No. HEI 4-109,266 discloses a still further developing device in which an irregularity area is formed on the surface of a supply member, and the following relationships exist between a rotational velocity V.sub.1 [mm/sec] of a toner carrier, a rotational velocity V.sub.2 [mm/sec] of the supply member, a width a [mm] in the rotation direction of the contacting area between the toner carrier and the supply member, and the number of convex portions per unit length [portions/mm] of the irregularity area in the rotation direction of the supply member: EQU V.sub.2 .gtoreq.V.sub.1 /4,
and EQU 6.ltoreq.N*a*(V.sub.1 +V.sub.2)/V.sub.1 .ltoreq.40
In the prior art disclosed in Japanese Unexamined patent publications Nos. SHO 47-13,088 and SHO 47-13,089, however, tones is supplied with its gravity to the carrier, and therefore the following problems are produced: The development hysteresis (irregularities of a toner layer produced by an image pattern which has been used in immediately previous developing process) causes the density unevenness and a ghost. When white patterns where no image is formed are continued, the toner carry amount on the toner carrier is gradually increased to cause the density unevenness or the formation of a toner image in a nonimage area (background fogging). When the toner carry amount is changed, the rotation of the toner carrier changes in torque or rotation number, thereby producing the printing jitters. Accordingly, such a developing device has drawbacks that the density unevenness often occurs, that the resolution or definition is low, that images having many jitters are obtained, and that the reliability is low.
In the prior art disclosed in Japanese Unexamined patent publication No. SHO 55-77,764, a toner layer is formed (predevelopment) by applying a bias voltage between the toner carrier using a foam material and the supply member. This is effective in stably forming a toner layer on the toner carrier. However, this additionally requires a bias voltage source, causing the size of the developing device to be enlarged.
In the prior art disclosed in Japanese patent publication No. SHO 52-125,340, the provision of the adjust member can reduce the degree of the density unevenness or ghost due to the development hysteresis. When while no image is formed are continued, however, the toner carry amount is gradually increased to cause the density unevenness or the background fogging, thereby degrading the printing quality.
The prior art disclosed in Japanese Unexamined patent publication No. HEI3-155,575 is effective in preventing the hardening of the supply member and a so-called filming phenomenon from occurring. These are caused by the loading of toner into a foam material which is liable to occur when toner of a small particle size is used. However, the prior art has a drawback that the consumption hysteresis remains in the toner layer on the surface of the toner carrier so that, in the succeeding rotation period of the toner carrier, the consumption hysteresis of the previous developing process appears as a ghost.
The prior art disclosed in Japanese Unexmained patent publication No. HEI 4-109,266 has the following drawbacks: In the case where toner of a small size is used, relatively excellent images may be obtained when the number of developing processes remains to be a relatively small value. When a high-density solid image which is continuous in the developing direction is developed after a number of developing processes have been conducted, however, the density of the rear end of the solid image is reduced. The consumption hysteresis remains in the toner layer on the surface of the toner carrier so that, in the succeeding rotation period of the toner carrier, the consumption hysteresis of the previous developing process appears as a ghost.